The Third Generation Partnership Project (3GPP) is developing a Long Term Evolution (LTE) standard using a physical layer based on globally applicable evolved universal terrestrial radio access (E-UTRA). In the LTE Release-10 (Rel-10) specification, uplink control information (UCI) is conveyed between the wireless terminal, referred to as the user equipment (UE), and the base station, referred to as the eNB. The UCI consists of channel quality information (CQI), Precoding Matrix Information (PMI), rank indication (RI), and downlink ACK/NAK indicators. Channel quality information refers to the quality of the downlink channel, the channel from the eNB to UE, as well as recommendations on the precoding to be used by the eNB based on observations of the downlink channel by the UE. Rank indication information is a recommendation by the UE on the number of layers or information-bearing streams that can be supported in the downlink channel with spatial multiplexing or multiple-input multiple-out (MIMO) transmission. ACK/NAK indicators are used to notify the eNB of successful decoding of information packets, referred to as transport blocks, sent on the downlink. The transmission of UCI by the UE occurs in 1 ms time intervals, termed subframes which occur either periodically for the case of CQI and RI or a fixed time after a downlink transmission for ACK/NAK indication. In addition to UCI the UE also transmits user data on the uplink during subframes specified by a scheduling message sent by the eNB on a downlink control channel. The subframes in which UCI is transmitted may or may not coincide with subframes containing user data. When a subframe is to contain UCI only but is not scheduled for user data transmission, the UCI is sent on the physical uplink control channel (PUCCH) whose modulation and coding is tailored specifically for efficient transmission of the small payloads of uplink control signaling. Likewise when only user data and not UCI is to be transmitted in subframe, a physical channel termed the physical uplink shared channel (PUSCH) designed for typically larger and variable sized payloads is used. The remaining case is when both UCI and user data are to be sent in the same subframe. There are several possibilities to utilize the PUCCH and PUSCH to accomplish this. First, both the PUCCH and PUSCH can be transmitted simultaneously. However both of these physical channels use Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-SOFDM) modulation or the Single-carrier Frequency Division Multiple Access (SC-FDMA) which has the desirable property that it yields time-domain signals whose envelopes have a low peak-to-average ratio and therefore can be amplified with high efficiency power amplifier while still meeting distortion and out-of-band requirements. The low peak-to-average property is compromised however when two DFT-SOFDM signals are transmitted simultaneously. The second alternative is to multiplex UCI and user data onto a single PUSCH. The LTE downlink transmission is based on Orthogonal Frequency Division Multiplexing (OFDM).
Multiplexing control information and user data onto a single DFT-SOFDM modulated channel has its own challenges however, control channel information must be able to be decoded reliably—a 0.01 to 0.0001 is a typical error rate—while at the same time maximizing the efficiency of user data transmission which, due to channel coding, can have symbol error rates as large as 0.1. Different types of UCI may have different reliability requirements, i.e. for CQI, a higher error rate such as 0.01 may be tolerable but for Rank and A/N, lower error rates such as 0.001˜0.0001 may be preferable because the system throughput loss may be severe otherwise. The control information and user data may also have different latency requirements which requires that different receiver types with different performance be used on PUSCH symbols used for UCI vs. symbols used for channel coded user data.
When spatial multiplexing transmission is performed on the PUSCH the multiplexing of UCI and user data has several unique challenges. Spatial multiplexing refers to the transmission of more than one symbol stream from multiple transmission antennas. In such a case, there is a need for a method and apparatus to determine how uplink control information may be multiplexed with uplink data.
The various aspects, features and advantages of the invention will become more fully apparent to those having ordinary skill in the art upon a careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.